Method of electrolytic production of high purity beryllium



1967 TAKAO NAKAMURA 3,296,107

METHOD OF ELECTROLYTIC PRODUCTION OF HIGH PURITY BERYLLIUM Filed Feb. 4. 1965 INVENTOR ATTORNEYS United States Patent 3,296,107 METHOD OF ELECTROLYTIC PRODUCTION OF HIGH PURITY BERYLLIUM T akao Nakamura, Mizuho-ku, Nagoya, Japan, assignor to NGK Insulators, Ltd., Mizuho-ku, Nagoya, Japan, a corporation of Japan Filed Feb. 4, 1963, Ser. No. 255,909 Claims priority, application Japan, Apr. 14, 1962,

37/ 15,095 3 Claims. (Cl. 204-65) The present invention relates to a method of electrolytic production of high purity beryllium from crude beryllium chloride.

Beryllium has the highest melting point 1285 C.) among light metals and has a small density (1.85 g./cm. and also mechanical strength comparable to mild steel so that it is a useful material for airplanes and is considered an indispensable material for space development. Moreover, beryllium has excellent nuclear properties and the smallest absorption cross section of thermal neutron and a large scattering cross section among metals so that it has been developed for use in atomic reactors and in X-ray tube windows, since its X-ray permeability is very high.

As above described, beryllium has excellent properties and may be used for various purposes, but it has the disadvantage that high purity beryllium cannot be obtained easily at a loW cost so that it cannot fulfill various demands.

The methods of obtaining metallic beryllium used at present for commercial purposes are classified into two methods; i.e., reduction of beryllium fluoride with magnesium and electrolysis of beryllium chloride. According to the method of magnesium reduction of beryllium fluoride, beryllium can be obtained at a comparatively low cost, yet it hasthe disadvantage of low purity. On the other hand, the electrolytic method gives a very'high purity product, but it has the disadvantage that the production cost is too high so that the above two methods are not satisfactory.

The principal object of the invention is to improve the above electrolysis by obviating the former disadvantages and to provide a more economical method.

In a conventional electrolysis, at first, crude beryllium chloride was obtained by chlorinating beryllium oxide of commercial purity. Since crude beryllium chloride contains substantial amounts of chlorides of iron, aluminum, silicon, copper and the like, it is necessary to purify it by distillation to obtain high purity beryllium chloride which is mixed with about the same quantity of sodium chloride and the mixture is fused in an electrolytic cell made of nickel and then a nickel cylinder is put in the electrolytic cell and it is used as a cathode to carry out the electrolysis with a graphite rod arranged in the middle of the cathode as an anode and metallic beryllium flake is electrolytically deposited on the inner surface of the nickel cylinder acting as a cathode. After the completion of electrolysis the nickel cathode on which beryllium flake has deposited is taken out of the electrolytic cell and the flake is collected and water washed'and dried to obtain metallic beryllium flake.

Alternatively, instead of refining crude beryllium chloride by distillation it is mixed with sodium chloride directly and fused in an electrolytic cell made of nickel and the fused salt is refined by means of a pre-electrolysis. This step is carried out by inserting a nickel cylinder into the electrolytic cell and the electrolysis is carried out by using the nickel cylinder as a cathode and by applying a voltage lower than the electrolytic deposition voltage of beryllium or at a little higher voltage to electrolytically deposit metallic impurities which are more electro-positive Patented Jan. 3, 1967 than beryllium, such as iron, aluminum, silicon, copper and nickel contained in the fused salts and removed together with the nickel cathode. Then it is replaced by a new cathode to electrolytically deposit metallic beryllium flake of higher purity and after the removal of the above impurities, crude beryllium chloride corresponding to beryllium chloride consumed in the electrolytic cell is supplied and the above described process is repeated to yield beryllium flake semicontinuously.

According to the conventional process the cost becomes higher due to the purification of crude beryllium chloride by distillation in a distillator and it accompanies a certain amount of loss of material so that its yield is poor.

On the other hand, according to the latter method, instead of refining beryllium chloride by distillation it needs another step of preelectrolysis so that the electrolysis is carried out in two stages which makes the operation complicated by interrupting the electrolysis for interchanging the nickel cathode and also there is danger of contacting the vapor of beryllium chloride in case of interchanging the nickel cathode so that it is not desirable due to the poisonous nature of beryllium. Moreover, when preelectrolysis cathode is taken out, a substantial amount of the fused salt adheres to the cathode so that there is large loss of the fused salt.

According to the invention the disadvantage of the conventional process can be obviated and the electrolysis can be carried out by only one step to collect beryllium flake of high purity at a high yield easily from raw beryllium chloride, that is, according to the invention, the preelectrolysis step and the normal electrolysis step can be carried out through a single step by using the same nickel cathode and after the completion of electrolysis the impure beryllium deposited during the preelectrolysis and the high purity flake can be easily separated.

The crude beryllium chloride to be used in the method of the invention is prepared by using commercial beryllium oxide containing a small quantity of chlorides of Fe, Al, Cu and Si in addition to beryllium chloride. The crude beryllium chloride is mixed with sodium chloride and charged into a nickel electrolytic cell and fused at a temperature of 300 to 400 C., then a cylindrical nickel cathode is inserted into the electrolytic cell and electrically connected to the cell. A graphite rod is inserted through a middle portion of the cover of the nickel cell electrically insulated from the cover. The graphite rod is connected to the positive side of a source of direct current and the electrolytic cell made of nickel to the negative side of the source. Under such condition, the interpolar voltage is maintained at a voltage (1.95 to 2.5 v.) a little higher than the decomposition voltage 1.95 v.) of beryllium chloride and the electrolysis is carried out by adjusting the current density of the cathode to 5 ma./cm. -30 ma./cm. Then beryllium containing a substantial amount of metal elements which are more electrochemically positive than beryllium, such as Fe, Al, Si, Cu, etc. deposits on the surface of nickel cathode substantially uniformly and tightly adheres thereto. After continuing the electrolysis for a time corresponding to the quantity of impurities contained in the electrolytic bath and when the above impure elements in the bath have been segregated out up to a necessary extent together with beryllium, the electrolysis is carried out by increasing the voltage and the current density up to a predetermined value of 30 to ma./cm. The time for efiecting electrolysis at the low voltage and low current is several to more than ten hours when the electrolytic bath is regulated again and 3 to 5 hours when the beryllium chloride is supplied.

By the above operation coarse and large crystals of high purity beryllium grow on the impure beryllium tightly adhered to the surface of the cathode in case of the initial low voltage and low current density. After a certain time of electrolysis when a necessary amount of metallic beryllium flake has grown the direct current source is shut down and the nickel cathode on which the flake has deposited is taken out of the cell and cooled to room temperature, then dipped into water to wash out the electrolyte adhered to the flake and metallic beryllium flake is scraped off. In this case, impure beryllium tightly adhered to the cathode surface by the initial electrolysis at a low voltage and low current density cannot be taken off by such usual scratching and only the metallic beryllium flake of high purity which had fully grown up is scraped off easily so that by this operation the well grown beryllium flake of high purity can easily be separated from the impure beryllium flake tightly adhered to the cathode. The high purity beryllium thus scraped off, if necessary, is washed and purified by means of caustic soda, nitric acid or oxalic acid, then washed with water, and alcohol, and dried. On the other hand, the beryllium of lower purity tightly adhered to the cathode is impossible to be scraped off as it is so tightly adhered and it is recovered as a solution by dissolving into hydrochloric acid or can be separated from the cathode as a thin flake by treating with dilute nitric acid and may be used as beryllium for making alloys. By supplying beryllium chloride corresponding to the electrolyzed beryllium, sodium chloride and beryllium chloride corresponding to the electrolyte taken out of the cell by adhering to the cathode and flake the electrolysis is continued in the similar manner as above described.

In order to positively carry out the above process and to positively separate the large high purity beryllium it is most important to carry out the electrolysis at first at a low voltage and low current density as above described. If, on the contrary, the electrolysis is effected from the first at a high voltage and high current density (normal voltage and current density) the impure beryllium containing a large amount of impure elements deposits at first on the cathode in a soft spongy state and large crystals grow thereon so that when the flake is scraped off the impure portion enters into the product to lower the purity.

For a better understanding of the invention, reference is made to the accompanying sketches, of which FIG; 1 illustrates a partial sectional view of the state of growth of beryllium flake on the surface of a cathode cylinder by a conventional method and FIG. 2 illustrates a similar sectional view showing the manner of growth of crystallized beryllium by the method of the invention.

Referring to the drawing, 1 represents a part of a nickel cylinder constituting a cathode, 2 large flakes of high purity beryllium, 3 soft spongy flake containing substantial amount of impurities, 4 tightly adhered flake containing impurities which cannot be scraped off, 5 represents tightly adhered low purity flake and 6 a scraping tool.

As above described the conventional method took two steps wherein impure elements are segregated out by preelectrolysis, then the electrolysis is stopped for taking out the cathode on which impure elements have deposited, then further electrolyzing by inserting a cathode into the cell. On the other hand, according to the method of the invention, the above two steps of the process are simplified by a single step so that the operation becomes very simple and the loss of electrolyte taken out by adhering to the preelectrolysis cathode is eliminated and the high purity flake deposited at first is not deteriorated by the nickel cathode since the high purity flake is directly predeposited on the inner surface of a new nickel cathode at the initial period of the normal electrolysis and there is no flake not recovered by firmly adhering to the cathode surface in the spongy shape and the high purity flake comparable to that of the conventional process can be yielded so that the present methods has many advantages in the improvement of easy operation and yielding uniform quality.

i values:

Fe, Al, Si, 11, Ni, percent percent percent percent percent Conventional method (two steps) 0. 012 0. 0062 0. 012 O. 004 0. 008 Large flake (the invention) 0. 016 0. 008 0. 010 0. 004 0. 006 Portion adhered to cathode (the invention) 0. 08 0. 028 0. 030 0. 075 0. 062

4 The invention will be explained further in detail by the example.

Example 5.7 kg. of industrial beryllium chloride and 4.3 kg. of sodium chloride were well-mixed and charged into a nickel electrolytic cell of 180 mm. inner diameter and heated from its outside by electric source and fused by maintaining the temperature at 350 C., then a nickel cathode having external diameter of 175 mm. and a graphite anode of 1.5 in. diameter were fitted at middle of the cell. Under such condition electric current of 10 a. was passed to make the current density at the cathode to 10 ma./cm. at an interpolar voltage of 2.4 v. Under such conditions, the electrolysis was conducted for three hours, then the voltage between two electrodes was raised up to 3.5 v. and a current of a. was passed to make the current density at the cathode to 80 ma./cm. and thus the electrolysis was conducted for 8 hours. After the direct current source was cut off, the cathode was lifted up and after cooling it was dipped into water and long grown flakes were scraped olf. After washing the thus obtained flake with 10% nitric acid, the flake was water washed and dipped into alcohol and then dried. Impure beryllium firmly adhered to the cathode was split off by dipping the cathode into 10% nitric acid and drying in the similar manner. The yield of the large flake scraped off at first was 89.4 g. and the weight of impure beryllium firmly adhered to the cathode was 5 g.

The yield of high purity beryllium flake having a large size obtained by the method of the invention was 72.2% by the calculation from the reduced weight of beryllium chloride during the electrolysis. When the electrolysis was carried out in two steps of preelectrolysis and the normal electrolysis the yield was 58 to 65% so that the present method of the invention shows an increase in yield of several to more than 10% The analysis of beryllium collected by the electrolysis showed the following Fe, A1, Si, Cu, Ni, percent percent percent percent percent Large flake 0. 010 0. 007 0. 011 0. 004 0. 005 Fine part 0. 024 0. 012 0.016 0. 008 0. 010

Total weight of the fine portion was 6 g.

I have described and illustrated a preferred embodiment of the invention. Those skilled in the art will see many modifications and uses for this invention which can be made without departing from its scope.

What I claim is:

1. A method of electrolytic production of high purity beryllium which comprises effecting electrolysis of a mixed fused salt of crude beryllium chloride and sodium chloride at first with a low current density through the cathode to deposit a first layer of beryllium flake containing a large amount of metallic impurities which are more electrolytically positive, than beryllium on the cathode,

then effecting further electrolysis by raising the current density through the cathode to deposit large substantially pure beryllium flakes on the previously deposited impure beryllium flake of the first layer, scraping ofl the large beryllium flake after completion of the electrolysis and leaving the first layer deposited on the cathode, recovering the large substantially pure beryllium flakes to obtain high purity beryllium from raw beryllium chloride.

2. A method according to claim 1, wherein the low current density through the cathode during the deposition of said first layer is about 5 to 30 ma./cm'. and wherein the current density through the cathode during said further electrolysis is about 30 to 120 ma./cm.

3. A method according to claim 1, further comprising maintaining the interpolar voltage during the deposition of the first layer between 1.95 and 2.5 volts, and raising the voltage for the further electrolysis to at least about 3.5 volts.

References Cited by the Examiner JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

1. A METHOD OF ELECTROLYTIC PRODUCTION OF HIGH PURITY BERYLLIUM WHICH COMPRISES EFFECTING ELECTROLYSIS OF A MIXED FUSED SALT OF CRUDE BERYLLIUM CHLORIDE AND SODIUM CHLORIDE AT FIRST WITH A LOW CURRENT DENSITY THROUGH THE CATHODE TO DEPOSIT A FIRST LAYER OF BERYLLIUM FLAKE CONTAINING A LARGE AMOUNT OF METALLIC IMPURITIES WHICH ARE MORE ELECTROLYTICALLY POSITIVE THAN BERYLLIUM ON THE CATHODE, THEN EFFECTING FURTHER ELECTROLYSIS BY RAISING THE CURRENT DENSITY THROUGH THE CATHODE TO DEPOSIT LARGE SUBSTANTIALLY PURE BERYLLIUM FLAKES ON THE PREVIOUSLY DEPOSITED IMPURE BERYLLIUM FLAKE OF THE FIRST LAYER, SCRAPING OFF THE LARGE BERYLLIUM FLAKE AFTER COMPLETION OF THE ELECTROLYSIS AND LEAVING THE FIRST LAYER DEPOSITED ON THE CATHODE, RECOVERING THE LARGE SUBSTANTIALLY PURE BERYLLIUM FLAKES TO OBTAIN HIGH PURITY BERYLLIUM FROM RAW BERYLLIUM CHLORIDE. 